Eye infection is a serious clinical problem, which has a high likelihood to lead to blindness without proper treatment. According to the Bulletin of the World Health Organization, eye infection lead to about 1 million new cases of blindness in Asia alone. One major cause of this serious disease is the infection caused by microorganisms such as bacteria and fungi, which usually occurs after intraocular surgery or simply is induced by a distant infective source in the body. Early diagnosis is critical in the management of this disease. The essential prerequisite for the optimal treatment of eye infection is to identify the microorganism causing infection as each type of microorganism causing eye infection requires a different therapeutic approach. For example, systemic antimicrobial therapy is usually recommended for patients with endogenous endophthalmitis. In this case, the type and extent of the infection needs to be diagnosed to determine potential complications and find underlying systemic cause or risk factors.
The current clinical procedure for identifying the microorganism species causing eye infection includes Gram staining and culture of aqueous and vitreous smear samples taken from the surface of infected eyes, which is typically performed in the pathology or microbiology department. Gram staining empirically differentiates bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls. It is fast and cheap. However, it is not meant to be a definitive tool for diagnosis. For example, it only works for bacteria and not every bacterium can be definitively classified. Culture is considered as the gold standard but this procedure is labor intensive and expensive. The cost for Gram staining and culture can range from about 60 Singapore dollars to about 180 Singapore dollars for material charge alone (excluding labor), not mentioning a much larger cost incurred for disease management if not treated in time and appropriately. It usually takes a few days to culture the microorganisms in smears to get reliable results. Such a long delay in diagnosis could result in the exacerbation of patients' symptoms. The delay may also lead to the optimal time frame for treatment being missed as well as the subsequent rising cost for disease management. In addition, taking smear samples from eyes for culturing is unpleasant and can be challenging in some patients. In addition to Gram staining and culturing, Polymerase Chain Reaction (PCR) is sometimes used to assist diagnosis especially for those species that cannot be cultured but PCR is in general expensive and its false-positive rate is often high.